LB's are generally the highest scoring IDP position.
Top LB's are (in order):
Of the DB's, Strong Safety is generally the most productive.
DL's are the lowest scoring position, unless you are required to carry a DL I wouldn't draft one outside the Top 10.
Go for those top LB's first. After the top 5-10 or so are taken, start digging into the DB's. One caveat....if you are required to have a DL or two, don't wait too long to grab one. The number of good, consistent DL's are very few, so you want to get a good one while you can, it's all about supply and demand. The pool of quality LB's and DB's is much deeper, higher supply for the demand, so wait on them and get a Top DL.
Seeing your scoring system, big plays aern't rewarded very generously over a simple solo tackle, this demotes the value of guys like DeMarcus Ware for whom that is their specialty...not so much racking up tackles. It also pulls down the value of the DL's who generally have value through big plays, they don't log alot of tackles like LB's and DB's (mainly safties) do. Top corners like Woodson, Winfield, Finnegan, Tillman, Leon Hall, R Marshall can buck this general safties score more than CB's rule.
One more thing. If your league rewards individual punt and kick return yardage, grab D Manning CHI, E Hobbs PHI, J Leonhard NYJ, T Williams GB - they are also return guys who are also starters at their defensive position. It is really only worthwhile to select these guys over more productive LB/DB options who don't return kicks if you get a point for about every 30 return yards or better. I'm in one league that scores 1 point for every 15 return yards, which is unusually generous scoring, so I have Ellis Hobbs and Tramon Williams on my roster, along with top guys Willis, Pollard, Vilma, Atogwe and Ryans.
Three 2009 Money Leagues.
Two 1st place, one 2nd place finish.